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Sleep Cycle Calculator
Best wake-up times based on 90-minute sleep cycles.
One sleep cycle ≈ 90 minutes. Waking at the end of 3–6 full cycles (4.5–9 hours) leaves you less groggy.
- Why 90-minute cycles?
- Sleep alternates between light, deep and REM stages in roughly 90-minute rounds. Waking mid-cycle interrupts deep sleep and causes grogginess.
- Is 5 cycles (7.5 hours) enough?
- The consensus recommendation for adults is 7–9 hours, which is 5–6 full cycles. Individual needs vary with age and lifestyle.
- What about naps?
- A 90-minute nap completes a full cycle; a 20-minute power nap stays out of deep sleep so you do not wake groggy.
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